Fluid flow controlling

1. The method of controlling flow including: providing a flow restrictor comprising a three-dimensional porous structure defining a through-flow matrix having a plurality of pores and having known pressure drop-flow rate characteristics; determining a desired rate of fluid flow through the flow restrictor; causing fluid to flow through the flow restrictor; determining the pressure drop across the flow restrictor of the fluid flowing therethrough; and adjusting the pressure drop across the flow restrictor of the fluid flowing through the flow restrictor such that the pressure drop of fluid across the flow restrictor corresponds to the desired rate of fluid flow.

2. The method of claim 1 including comparing the pressure drop of the fluid flowing through the flow restrictor with data representative of the known pressure drop-flow rate characteristics of the flow restrictor and adjusting the pressure of fluid upstream of said restrictor on the basis of said comparison.

3. The method of claim 1 including comparing the pressure drop of the fluid flowing through the flow restrictor with data representative of the known pressure drop-flow rate characteristics of the flow restrictor and adjusting the pressure of gas downstream of said restrictor on the basis of said comparison.

4. The method of claim 1 wherein said flow restrictor comprises porous sintered metal.

5. The method of claim 1 including providing a first sensor to determine the pressure of fluid upstream of said flow restrictor and to provide data indicative of said upstream pressure and a second sensor to determine the pressure of fluid downstream of said restrictor and provide data indicative of said downstream pressure, and wherein said pressure drop is determined on the basis of a comparison of said data.

6. The method of claim 5 including providing electronic signals indicative of the desired rate of fluid flow, of said data indicative of said upstream pressure, of said data indicative of said downstream pressure, and of said data representative of the known pressure drop-flow rate characteristics of the flow restrictor.

7. The method of claim 6 wherein the pressure of the fluid upstream or downstream of said flow restrictor is adjusted on the lower of said electronic signals.

8. The method of claim 1 including providing a pressure regulator to adjust said pressure of fluid upstream of said flow restrictor.

9. The method of claim 1 wherein the pressure drop across said flow restrictor is monitored substantially continuously over a period of time, and during said period the pressure drop of fluid flowing through said restrictor is adjusted as required to maintain fluid flow through said flow restrictor at substantially said desired rate of flow.

10. The method of claim 1 including providing a memory containing data indicative of said known pressure drop-flow rate characteristics and a first sensor providing data indicative of pressure of fluid upstream or downstream of said flow restrictor, and wherein the pressure drop of fluid flowing through said restrictor is adjusted based on said data contained in said memory and data provided by said first sensor.

11. The method of claim 10 including a second sensor providing data indicative of pressure of fluid downstream of said flow strictor, wherein first sensor provides data indicative of pressures of fluid upstream of said flow restrictor, and wherein said pressure drop of fluid flowing through said restrictor is adjusted based on said data contained in said memory and data provided by said first and second sensors.

12. The method of any of claims 1 - 11 wherein the fluid is a gas.